Optical module

ABSTRACT

Some embodiments of the present application provide an optical module, including: a master control chip, a laser transmitter, and a laser receiver; the laser transmitter and the laser receiver being connected to the master control chip, respectively; where the laser receiver includes: a PIN photodiode, a trans-impedance amplifier with a transimpedance of no less than 43K ohms, a lens, and a shell; the PIN photodiode being electrically connected to the trans-impedance amplifier; the PIN photodiode, the trans-impedance amplifier and the lens being encapsulated within the shell in a manner of transistor out-line; and the lens being coated with an antireflection film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201610184340.3, filed on Mar. 28, 2016, entitled “OPTICAL MODULE”, whichis hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present application relates to optical communication technologiesand, in particular, to an optical module.

BACKGROUND

With rapid development of the Internet, demands for network resourcesare growing rapidly, leading to ever increasing fiber to the home (FTTH)deployment scale. As a core part of optical fiber communication systems,optical modules are globally demanded in huge volume, which makes costcontrol of optical modules particularly important in the process ofdeveloping and manufacturing the optical modules.

SUMMARY

Some embodiments of the present application provide an optical module,including: a master control chip, a laser transmitter and a laserreceiver; the laser transmitter and the laser receiver being connectedto the master control chip, respectively; where the laser receiverincludes: a PIN photodiode, a trans-impedance amplifier with atransimpedance of no less than 43K ohms, a lens and a shell; the PINphotodiode being electrically connected to the trans-impedanceamplifier; the PIN photodiode, the trans-impedance amplifier and thelens being encapsulated within the shell in a manner of transistorout-line; and the lens being coated with an antireflection film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a circuit structure of anoptical module according to some embodiments of the present application;

FIG. 2 is a schematic structural diagram of a laser receiver of FIG. 1;

FIG. 3 is a sectional view of the laser receiver of FIG. 2 taken alongline A-A;

FIG. 4 is a perspective view illustrating an optical module according tosome embodiments of the present application;

FIG. 5 is an exploded view illustrating an optical module according tosome embodiments of the present application;

FIG. 6 is a schematic structural diagram of a BOSA of FIG. 5;

FIG. 7 is a schematic structural diagram of a master control chipaccording to some embodiments of the present application;

FIG. 8 is a schematic structural diagram of a master control chipaccording to some other embodiments of the present application; and

FIG. 9 is a schematic structural diagram of an optical module accordingto some embodiments of the present application.

Description of reference signs:  10-Master control chip;  20-Lasertransmitter;  30-Laser receiver;  31-PIN photodiode;  32-TIA;  33-Lens; 33-Antireflection film  34-Shell;  1-BOSA;  2-Housing;  3-Conductivegasket;  4-PCB;  5-Pin assembly;  6-BracketBracket;  7-Claw;  8-Tailplug; 101-Laser driver; 102-Receipt signal limiting amplifier;103-Microcontroller; 104-Internal storage device; 104-External storagedevice;  90-ROSA;  91-TOSA.

DESCRIPTION OF EMBODIMENTS

In order to make purposes, technical solutions and advantages of thepresent application clearer, the technical solutions in embodiments ofthe present application will be described with reference to theaccompanying drawings. Obviously, the described embodiments are onlypart of the embodiments of the present application, rather than all ofthem. According to the embodiments of the present application, all ofthe other embodiments obtained by those of ordinary skill in the artwithout creative effort should fall within the protection scope of thepresent application.

An optical module provided in some embodiments of the presentapplication may be applied to an optical network unit (ONU) in a gigabitcapable passive optical network (GPON) to achieve high data ratetransmission over long distance. Of course, the optical module may alsobe applied to an ONU in other passive optical networks (PON), such asEthernet passive optical network (EPON), for transmitting signalsthrough optical fibers.

FIG. 1 is a schematic diagram illustrating a circuit structure of anoptical module according to some embodiments of the present application,FIG. 2 is a schematic structural diagram of a laser receiver of FIG. 1,and FIG. 3 is a sectional view of the laser receiver of FIG. 2 takenalong line A-A. As shown in FIGS. 1-3, an optical module provided insome embodiments of the present application includes a master controlchip 10, a laser transmitter 20 and a laser receiver 30, the lasertransmitter 20 and the laser receiver 30 being connected to the mastercontrol chip 10, respectively; where the laser receiver 30 includes aPIN photodiode 31, a trans-impedance amplifier (TIA) 32 with atransimpedance of no less than 43K ohms, a lens 33 and a shell 34; thePIN photodiode 31 being electrically connected to the TIA 32; the PINphotodiode 31, the TIA 32 and the lens 33 being encapsulated within theshell 34 in a manner of transistor out-line; and the lens 33 beingcoated with an antireflection film 33′.

The master control chip 10 may be a highly integrated three-in-one chipin which a laser driver 101, a receipt signal limiting amplifier 102 anda microcontroller 103 are integrated. A storage device 104 of smallcapacity may be integrated in the master control chip 10, as shown inFIG. 7; or the master control chip 10 may be connected to an externalstorage device 104′, such as an electrically erasable programmableread-only memory (EEPROM), through a bus, as shown in FIG. 8. The lasertransmitter 20 may convert an electrical signal from the master controlchip 10 into an optical signal to be transmitted through an opticalfiber. The laser receiver 30 may convert an optical signal from theoptical fiber into an electrical signal to be transmitted to the mastercontrol chip 10.

The laser transmitter 20 and the laser receiver 30 may be encapsulatedin a transmitter optical subassembly (TOSA) 91 and a receiver opticalsubassembly (ROSA) 90, respectively, as shown in FIG. 9. Alternatively,the laser transmitter 20 and the laser receiver 30 may be encapsulatedtogether in a bi-directional optical sub-assembly (BOSA). To facilitatedescription, some embodiments of the present application will now beexplained by taking a BOSA as an example

The laser transmitter 20 may be configured to automatically control itsoptical power and extinction ratio by using closed-loop design ofoptical power, dual closed-loop design of optical power and extinctionratio, or open-loop design. In the closed-loop design of optical power,a backlight diode and a laser diode (LD) are integrated in the lasertransmitter 20, and the master control chip 10 automatically controlsthe power according to a bias current collected from the backlightdiode, so as to prevent unstable optical power caused by slopeefficiency changes of the LD as the temperature changes. Meanwhile, afirst lookup table (containing the correlation between a modulationcurrent and the temperature) is pre-generated based on characteristicsof the LD and stored in a storage device, and the table is queriedaccording to the temperature, so that the extinction ratio is maintainedstable under different temperatures. In the dual closed-loop design ofoptical power and extinction ratio, the master control chip 10 providesautomatic compensation according to changes of a bias current collectedfrom the backlight diode and a modulation current collected from the LD,so that both the optical power and the extinction ratio are kept stable.In the open-loop design, then instead of including a backlight diode inthe laser transmitter 20, a second lookup table (containing thecorrelation between the bias current and the temperature) needs to bepre-generated based on characteristics of the laser transmitter 20 andstored in a storage device, and the table is queried according to thetemperature, so that both the optical power and the extinction ratio aremaintained stable under different temperatures.

The master control chip 10 may implement direct control over the laserdriver 101 through an internal register, so as to achieve fast controlresponse. The register may timely control and change the laser driveraccording to different conditions of a continuously tracked ONUtemperature, a supply voltage, a laser bias current and a modulationcurrent, so as to ensure reliable operation of the optical module. Tomonitor received optical power, the master control chip 10 samples amonitored current output from the laser receiver 30, so that digitaldiagnosis may be enabled on the optical module. Additionally, atemperature sensor and an internal analog-to-digital converter (ADC) maybe integrated in the master control chip 10 to convert collected data,so that the temperature and voltage can be monitored.

In the laser receiver 30, the bandwidth of the PIN photodiode 31 may be2.5G, 10G or the like, and preferably 10G in this embodiment forensuring sufficient bandwidth. The trans-impedance amplifier 32 is ahigh gain TIA with a transimpedance of no less than 43K ohms, e.g. a TIA32 with a transimpedance of 51K ohms for ensuring better gain effect.

The PIN photodiode 31, the TIA 32 and the lens 33 of the laser receiver30 are encapsulated within the shell 34 in a manner of transistorout-line (TO), where the lens 33 may be hemispherical. For differentreceipt wavelengths, an anti-reflection film for a corresponding waveband may be coated on the lens 102, so as to reduce reflection of thereceived light, increase transmitted light, and hence increasesensitivity. For example, the antireflection film has a transmittance ofmore than 98%.

The high gain TIA 32 with a transimpedance of no less than 43K ohms cansufficiently amplify a weak electrical signal converted by the PINphotodiode 31, which increases the sensitivity of the laser receiver 30,thereby meeting the requirement of GPONs for long distances. That is, insome embodiments of the present application, the PIN photodiode 31combined with a super TIA may be used to provide transmission with highsensitivity and long distance in the GPONs.

According to some embodiments of the present application, an opticalmodule includes: a master control chip, a laser transmitter and a laserreceiver, the laser transmitter and the laser receiver being connectedto the master control chip, respectively, where the laser receiver isembodied as a PIN photodiode combined with a high gain trans-impedanceamplifier of no less than 43K ohms transimpedance. The optical modulecan provide transmission with high sensitivity and long distance in theGPONs while effectively lowering the cost. Additionally, anantireflection film is coated on a lens of the laser receiver to reducereflection of received light, increase transmitted light, therebyfurther increasing sensitivity.

FIG. 4 is a perspective view illustrating an optical module according tosome embodiments of the present application, and FIG. 5 is an explodedview illustrating an optical module according to some embodiments of thepresent application. Additionally, some embodiments of the presentapplication are described by taking a laser transmitter 20 and a laserreceiver 30 being encapsulated in a BOSA 1 as an example. FIG. 6 is aschematic structural diagram of a BOSA of FIG. 5. On the basis of theabove embodiment shown in FIG. 1, as shown in FIG. 5, in an opticalmodule according to some embodiments of the present application, aconductive gasket 3 is provided between a laser receiver 30 (which iscontained in a BOSA 1) and a housing 2 of the optical module.

The conductive gasket 3 may be conductive foam or conductive rubberetc., and be provided between the laser receiver 30 of the BOSA 1 andthe housing 2 (i.e. between the BOSA 1 and the housing 2 shown in FIG.4), so that the laser receiver 30 is sufficiently in touch with thehousing 2 so as to shorten the length of a ground loop, maintain astable ground level reference, avoid introducing a ground noise whichwill interfere with a received high-frequency signal, thereby furtherimproving sensitivity.

In some embodiments of the present application, the master control chip10 is provided on a printed circuit board (PCB) 4 of the optical module,the PCB 4 being electrically connected to the laser transmitter 20 andthe laser receiver 30.

In some embodiments of the present application, the optical module maybe of a pluggable structure or a pigtail structure. In some embodimentsof the present application, the optical module is described by taking apluggable structure as an example. The PCB may be a two-layer board, afour-layer board or a six-layer board, etc.

If the optical module is of a pluggable structure, the PCB 4 may bedesigned as a four-layer board to lower cost. For impedance matching, acomplete ground plane can be provided on the second layer to minimizethe length of the ground loop, so as to improve the capacity ofresisting interference and reduce radiation.

If the optical module is of a pigtail structure, the PCB 4 may bedesigned as a two-layer board to lower the cost. For impedance matching,a high rate signal line for signal reception may be copper-plated onboth its upper and lower sides, and a ground plane may be laid toinclude evenly distributed vias so as to minimize the length of theground loop, which helps improving the capacity of resistinginterference and reducing radiation.

In some embodiments of the present application, the optical modulefurther includes a pin assembly 5, a bracket 6, a claw 7, and a tailplug 8, where one end of the pin assembly 5 is welded on the PCB 4 andthe other end is provided passing through the bracket 6, the lasertransmitter 20 and the laser receiver 30 are fixed between the housing 2and the bracket 6 by the claw 7, and one end of the tail plug 8 isprovided within the claw 7.

The pin assembly 5 may include 20 PINs, with one end welded on the PCB4, and the other end passing through the bracket 6 to connect to a mainboard to allow for signal transmission.

One end of the BOSA 1 is welded on the PCB 4 and the other end is fixedin the claw 7 which is clamped between the housing 2 and the bracket 6,so as to fix the BOSA 1 within a tube formed by the housing 2 and thebracket 6.

The outward facing end of the claw 7 is plugged by the tail plug 8 toward off dust.

In an optical module according to some embodiments of the presentapplication, a conductive gasket is provided between a laser receiverand a housing so as to enable the laser receiver to be sufficiently intouch with the housing, thereby shortening the length of a ground loopand improving sensitivity.

Finally, it should be noted that the foregoing embodiments are merelyintended for describing the technical solutions of the presentapplication rather than limiting the present application. Although thepresent application is described with reference to the foregoingembodiments, persons of ordinary skill in the art should understand thatthey may still make modifications to the technical solutions describedin the foregoing embodiments, or make equivalent replacements to some orall technical features therein; however, these modifications orreplacements do not make the essence of corresponding technicalsolutions depart from the scope of the technical solutions in theembodiments of the present application.

What is claimed is:
 1. An optical module, comprising: a master controlchip, a laser transmitter and a laser receiver, the laser transmitterand the laser receiver being connected to the master control chip,respectively, wherein the laser receiver comprises a PIN photodiode, atrans-impedance amplifier with a transimpedance of no less than 43Kohms, a lens and a shell, the PIN photodiode being electricallyconnected to the trans-impedance amplifier, and the PIN photodiode, thetrans-impedance amplifier and the lens being encapsulated within theshell in a manner of transistor out-line.
 2. The optical moduleaccording to claim 1, wherein a conductive gasket is provided betweenthe laser receiver and a housing of the optical module.
 3. The opticalmodule according to claim 2, wherein the conductive gasket comprisesconductive foam or conductive rubber.
 4. The optical module according toclaim 1, further comprising: a printed circuit board (PCB) on which themaster control chip is provided, wherein the PCB is electricallyconnected to the laser transmitter and the laser receiver.
 5. Theoptical module according to claim 4, wherein the optical module is of apluggable structure, and the PCB is a four-layer board.
 6. The opticalmodule according to claim 4, wherein the optical module is of a pigtailstructure, and the PCB is a two-layer board.
 7. The optical moduleaccording to claim 5, further comprising: a pin assembly, a bracket, aclaw and a tail plug, wherein one end of the pin assembly is welded onthe PCB and the other end is provided passing through the bracket; thelaser transmitter and the laser receiver are fixed between the housingand the bracket by the claw; and one end of the tail plug is providedwithin the claw.
 8. The optical module according to claim 1, wherein thelaser transmitter is encapsulated in a transmitter optical subassembly(TOSA) and the laser receiver is encapsulated in a receiver opticalsubassembly (ROSA).
 9. The optical module according to claim 1, whereinthe laser transmitter and the laser receiver are encapsulated in abi-directional optical sub-assembly (BOSA).
 10. The optical moduleaccording to claim 1, wherein a laser driver, a receipt signal limitingamplifier and a microcontroller are integrated in the master controlchip.
 11. The optical module according to claim 10, wherein a storagedevice is integrated in the master control chip.
 12. The optical moduleaccording to claim 10, wherein the master control chip is connected to astorage device through a bus.
 13. The optical module according to claim1, wherein the trans-impedance amplifier has a transimpedance of 51Kohms.
 14. The optical module according to claim 1, wherein the lens iscoated with an antireflection film.
 15. The optical module according toclaim 1, wherein the PIN photodiode has a positive pole connected to apositive pole of the photodiode.